Phosphate-containing surfactants for use with pigment—and latex-containing ink-jet inks

ABSTRACT

The present disclosure is drawn to an ink-jet ink and a method of ink-jet printing over a prolonged period of time. The ink-jet ink include from 0.1 wt % to 10 wt % pigment by solids, from 0.1 wt % to 15 wt % latex by solids, and from 0.01 wt % to 3 wt % phosphate-containing surfactant, wherein when the ink-jet ink is fired from a thermal ink-jet printhead at 400 million drops per nozzle with said nozzle having an orifice size of about 20 microns, at least 80% drop weight is retained compared to an initial firing prior to firing the 400 million drops per nozzle.

BACKGROUND

There are several reasons that ink-jet printing has become a popular wayof recording images on various media surfaces, particularly paper. Someof these reasons include low printer noise, capability of high-speedrecording, and multi-color recording. Additionally, these advantages canbe obtained at a relatively low price to consumers. Though there hasbeen great improvement in ink-jet printing, accompanying thisimprovement are increased demands by consumers in this area, e.g.,higher speeds, higher resolution, full color image formation, increasedstability, etc. As new ink-jet inks are developed, there have beenseveral traditional characteristics to consider when evaluating the inkin conjunction with a printing surface or substrate. Suchcharacteristics include edge acuity and optical density of the image onthe surface, black to color bleed control, dry time of the ink on thesubstrate, adhesion to the substrate, lack of deviation in ink dropletplacement, presence of all dots, resistance of the ink after drying towater and other solvents, long term storage stability, and long termreliability without corrosion or nozzle clogging. Though the above listof characteristics provides a worthy goal to achieve, there aredifficulties associated with satisfying all of the abovecharacteristics. Often, the inclusion of an ink component meant tosatisfy one of the above characteristics can prevent anothercharacteristic from being met. Thus, most commercial inks for use inink-jet printers represent a compromise in an attempt to achieve atleast an adequate response in meeting all of the above listedrequirements.

A few characteristics of ink-jet printing systems that are desirable toachieve are related to nozzle health, kogation, and ink throughput. Withrespect to this, obtaining acceptable print quality while retainingacceptable printing reliability and nozzle health is a constantchallenge in the ink-jet printing industry. Accordingly, investigationscontinue into developing ink formulations that can be printed accuratelyand with acceptable durability without excessive clogging or orificekogation.

DETAILED DESCRIPTION

Before the present invention is disclosed and described, it is to beunderstood that this invention is not limited to the particularstructures, process steps, or materials disclosed herein, but isextended to equivalents thereof as would be recognized by thoseordinarily skilled in the relevant arts. It should also be understoodthat terminology employed herein is used for the purpose of describingparticular embodiments only and is not intended to be limiting.

In describing and claiming the present invention, the followingterminology will be used in accordance with the definitions set forthbelow.

It is noted that, as used in this specification and the appended claims,the singular forms “a,” “an,” and “the” include plural referents unlessthe context clearly dictates otherwise. Thus, for example, reference to“an ink” includes one or more of such inks, reference to “a pigment”includes reference to one or more amounts of pigments, and reference to“the ink set” includes reference to one or more ink sets.

As used herein, “liquid vehicle” or “ink vehicle” refers to the liquidfluid in which colorant is dispersed or dissolved to form an ink. Liquidvehicles are well known in the art, and a wide variety of ink vehiclesmay be used in accordance with embodiments of the present invention.Such liquid vehicles may include a mixture of a variety of differentagents, including without limitation, surfactants, organic co-solvents,buffers, biocides, viscosity modifiers, sequestering agents, stabilizingagents, and/or water. The liquid vehicle can also carry other additivessuch as latex particulates and other polymers, in some embodiments.

As used herein, “ink” refers to a single liquid vehicle that contains atleast one colorant, and in accordance with embodiments of the presentinvention, certain inks will include a pigment and latex.

As used herein, “latex,” “latex polymer,” or “latex particles” refer tothe polymeric masses synthesized from individual monomers, which can bedispersed in a liquid vehicle forming a latex dispersion. The term“latex” generally refers to liquid and polymeric particles that aredispersed within the liquid. However, when a latex is formulated withinan ink, the liquid becomes part of the liquid vehicle of the ink, andthus, latex polymer can be described based on the latex particle orlatex polymer solids that remain dispersed in the liquid vehicle.Latexes do not included polymers that are completely dissolved in aliquid vehicle.

As used herein, “pigment” refers to a colorant particle which istypically substantially insoluble in the liquid vehicle in which it isused. Pigments can be conventionally dispersed using a separatedispersing agent, or can be self-dispersed, having a dispersing agentattached to the surface of the pigment.

As used herein, “self-dispersed” generally refers to pigments that havebeen functionalized with a dispersing agent, such as by chemicalattachment of the dispersing agent to the surface of the pigment. Thedispersing agent can be a small molecule or a polymer or oligomer. Thedispersing agent can be attached to such pigments to terminate the outershell of the pigment with a charge, thereby creating a repulsive naturethat reduces agglomeration of pigment particles within the liquidvehicle.

As used herein, the term “about” is used to provide flexibility to anumerical range endpoint by providing that a given value may be “alittle above” or “a little below” the endpoint. The degree offlexibility of this term can be dictated by the particular variable andwould be within the knowledge of those skilled in the art to determinebased on experience and the associated description herein.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary.

Concentrations, amounts, and other numerical data may be expressed orpresented herein in a range format. It is to be understood that such arange format is used merely for convenience and brevity and thus shouldbe interpreted flexibly to include not only the numerical valuesexplicitly recited as the limits of the range, but also to include allthe individual numerical values or sub-ranges encompassed within thatrange as if each numerical value and sub-range is explicitly recited. Asan illustration, a numerical range of “about 1 wt % to about 5 wt %”should be interpreted to include not only the explicitly recited valuesof about 1 wt % to about 5 wt %, but also include individual values andsub-ranges within the indicated range. Thus, included in this numericalrange are individual values such as 2, 3.5, and 4 and sub-ranges such asfrom 1-3, from 2-4, and from 3-5, etc. This same principle applies toranges reciting only one numerical value. Furthermore, such aninterpretation should apply regardless of the breadth of the range orthe characteristics being described.

In accordance with this, it has been recognized that pigmented ink-jetinks which include latex particulates can clog internal ink channels,firing chambers, or nozzles, leading to resistor kogation due tostarvation of the ink flow or impeded drop ejection, and that thisphenomenon can be reduced by including a phosphate-containing surfactantin the ink-jet ink formulation. It has likewise been discovered thatinks containing pigment and latex or other dispersed polymers tend tosuffer from kogation of resistors due to buildup of polymeric binder orpigment on the resistor, resulting in shortened lifetime of theprinthead and decreased print quality at earlier stages in the life ofthe printhead. The introduction of a phosphate-containing surfactant canameliorate or even substantially eliminate clogging from polymer buildupat the printhead orifices and/or kogation of resistors fromlatex-containing inks arising from either process, thus extending thelife of ink-jet pens in general (and particularly thermal ink-jet pens)which carry such inks. Without being bound by any particular theory, itis thought that the addition of a phosphate-containing surfactantinduces particle-ink vehicle separation of the latex particulates fromthe liquid vehicle, a process normally seen only with certain pigmentparticles, and only during periods of non-ejection or low duty cyclewhen evaporation of water from nozzles can be significant. Thisseparation prevents or reduces unwanted migration, enrichment, anddestabilization of the latex particulates in the printhead nozzles,internal ink channels, or firing chambers, thus contributing tounimpeded drop ejection and the increased nozzle health observed whenthese surfactants are included. Alternatively or in conjunction withthis, the phosphate-containing surfactant may directly interfere withdeposition of polymeric or pigment particles that can form films on thethermal ink-jet resistor during unimpeded ink flow and firing, leadingto kogation and reduced drop ejection quality.

Thus, an ink-jet ink can comprise from 0.1 wt % to 10 wt % pigment bysolids, from 0.1 wt % to 15 wt % latex by solids, and from 0.01 wt % to3 wt % phosphate-containing surfactant.

In another embodiment, a method of printing over a prolonged period oftime with enhanced ink-jet architecture reliability can comprise jettingan ink-jet ink onto a media substrate. The ink-jet ink can comprise from0.1 wt % to 10 wt % pigment by solids, from 0.1 wt % to 15 wt % latex bysolids, and from 0.01 wt % to 3 wt % phosphate-containing surfactant.The jetting can be such that the ink does not substantially contributeto nozzle clogging and/or related resistor kogation.

Though this ink in each of these embodiments can be fired from a varietyof different types of ink-jet architecture, as a definitional matter,when the ink-jet ink is fired from a thermal ink-jet printhead at 400million drops per nozzle, at least 80% drop weight is often retainedcompared to an initial firing prior to firing the 400 million drops pernozzle. These measurements can be based on a printhead having an orificesize of about 20 microns (based on the longest distance across theorifice, such as diameter when the orifice has a circular shape), oralternatively, can be based on starting drop weights of about 11 ng to12 ng. In another embodiment, when the ink-jet ink is fired from athermal ink-jet printhead at 400 million drops per nozzle, at least 90%drop weight can be retained compared to an initial firing prior tofiring the 400 million drops per nozzle. It is emphasized that thesenumbers and testing protocols are in no way limiting as to how theink-jet inks of the present invention are to be fired or jetted. Rather,these numbers merely set forth testing protocols that one can use todetermine whether an ink-jet ink meets the criteria set forth herein.For example, the inks of the present invention can be fired from thermalink-jet architecture or piezo ink-jet architecture. Exemplary orificesizes that are particularly useful include those ranging from 10 micronsto 40 microns, though sizes outside of this range are also usable.Exemplary drop weights (when jetting) for the inks of the presentdisclosure can range from 2 ng to 40 ng, though drop weights outside ofthis range can also be used. Thus, the 20 micron orifice and/or the“about 11 ng to 12 ng” parameters set forth above are merely provided toset forth testing protocols to determine performance characteristics ofink-jet inks, as will be further exemplified in the Examples herein.

It is also noted that drop velocity change is also valuable indetermining nozzle health in general. As such, in each of theseembodiments, at least 75% drop velocity can be retained compared to theinitial firing prior to firing the 400 million drops per nozzle; atleast 80% drop velocity can be retained compared to the initial firingprior to firing the 400 million drops per nozzle; or often, at least 90%drop velocity can be retained compared to the initial firing prior tofiring the 400 million drops per nozzle.

Though the testing conditions for the inks described herein wereconducted using thermal ink-jet architecture having 20 micron-sizedprinting nozzles, other sizes of nozzles can be used, e.g., 5 microns to100 microns, or from 10 microns to 40 microns. Also, various printingtemperatures that are typical for thermal ink-jet architecture can alsobe used with acceptable results.

It is also noted that in each of these embodiments, the pigment contentcan alternatively be from 0.5 wt % to 5 wt %, the latex solids contentcan be from 2 wt % to 8 wt %, and/or the phosphate-containing surfactantcontent can be from 0.3 wt % to 1 wt %.

In accordance with the embodiments described herein, various details areprovided herein which are applicable to each of the ink-jet ink or inks,method of printing, etc. Thus, discussion of one specific embodiment isrelated to and provides support for this discussion in the context ofthe other related embodiments.

Pigments

The pigments that can be used in accordance with embodiments of thepresent disclosure include both self-dispersed pigments as well asconventionally dispersed pigments, e.g., pigments dispersed by aseparate dispersing agent that is not covalently attached to thesurface. If self-dispersed, a dispersant is typically prepared in aprecursor form, and then the precursor is attached to the pigment tochemically modify the surface of the pigment. In one embodiment, thedispersant can be attached to the pigment using various precursormaterials, such as para-aminobenzoic acids, isophthalic acids,tricarboxylic acids, carboxylic groups, sulfonylic groups, phosphates,oligomers, polymers, and isomers thereof, for example. Other precursorscan also be used to attach to the pigment, as would be known by thoseskilled in the art.

As alluded to, pigment colorant can be used in accordance withembodiments of the present disclosure. Specifically, if black is used,the black pigment can be any commercially available black pigment thatprovides acceptable optical density and print characteristics. Suchblack pigments can be manufactured by a variety of known methods such aschannel methods, contact methods, furnace methods, acetylene methods, orthermal methods, and are commercially available from such vendors asCabot Corporation, Columbian Chemicals Company, Evonik, Mitsubishi, andE.I. DuPont de Nemours and Company. For example, commercially availablecarbon black pigments include Color Black FW 200, Color Black FW 2V,Color Black FW1, Color Black FW 18, Color Black FW S160, Color Black FWS170, Printex including 95, 85, 75, 55, 45, 300, 35, 25, 200, 12, andSpecial Blacks including, 4A, 4, 5, 6, 550, 350, 250; BP1100, BP900,BP800, M1100, M900, M800, Monarch 1400, Monarch 1300, Monarch 1100,Monarch 1000, Monarch 900, Monarch 880, and Monarch 700; Cab-O-Jet 200and Cab-O-Jet 300; Raven 2500ultra, Raven 2000, Raven 7000, Raven 5750,Raven 5250, Raven 5000, and Raven 3500; 45 B, and combinations thereof.

In addition to black, other pigment colorants can be used, such as cyan,magenta, yellow, blue, orange, green, pink, etc. Suitable organicpigments include, for example, azo pigments including diazo pigments andmonoazo pigments, polycyclic pigments (e.g., phthalocyanine pigmentssuch as phthalocyanine blues and phthalocyanine greens, perylenepigments, perynone pigments, anthraquinone pigments, quinacridonepigments, dioxazine pigments, thioindigo pigments, isoindolinonepigments, pyranthrone pigments, and quinophthalone pigments), insolubledye chelates (e.g., basic dye type chelates and acidic dye typechelate), nitropigments, nitroso pigments, anthanthrone pigments such asPR168, and the like. Representative examples of phthalocyanine blues andgreens include copper phthalocyanine blue, copper phthalocyanine greenand derivatives thereof (Pigment Blue 15 and Pigment Green 36).Representative examples of quinacridones include Pigment Orange 48,Pigment Orange 49, Pigment Red 122, Pigment Red 192, Pigment Red 202,Pigment Red 206, Pigment Red 207, Pigment Red 209, Pigment Violet 19 andPigment Violet 42. Representative examples of anthraquinones includePigment Red 43, Pigment Red 194, Pigment Red 177, Pigment Red 216 andPigment Red 226. Representative examples of perylenes include PigmentRed 123, Pigment Red 149, Pigment Red 179, Pigment Red 190, Pigment Red189 and Pigment Red 224. Representative examples of thioindigoidsinclude Pigment Red 86, Pigment Red 87, Pigment Red 88, Pigment Red 181,Pigment Red 198, Pigment Violet 36, and Pigment Violet 38.Representative examples of heterocyclic yellows include Pigment Yellow1, Pigment Yellow 3, Pigment Yellow 12, Pigment Yellow 13, PigmentYellow 14, Pigment Yellow 17, Pigment Yellow 65, Pigment Yellow 73,Pigment Yellow 74, Pigment Yellow 90, Pigment Yellow 110, Pigment Yellow117, Pigment Yellow 120, Pigment Yellow 128, Pigment Yellow 138, PigmentYellow 150, Pigment Yellow 151, Pigment Yellow 155, and Pigment Yellow213. Such pigments are commercially available in either powder, presscake, or dispersion form from a number of sources.

Typically, the pigments of the present invention can be from about 5 nmto about 10 μm, and in one aspect, the pigments can be from 10 nm toabout 500 nm in size, although sizes outside this range can be used ifthe pigment can remain dispersed and provide adequate printingproperties.

Latexes

Latexes include both latex particulates as well as the aqueous medium inwhich the latex particulates are dispersed. More specifically, a latexis a liquid suspension comprising a liquid (such as water and/or otherliquids) and polymeric particulates from 20 nm to 500 nm (and often from100 nm to 300 nm) in size. Typically, the polymeric particulate can bepresent in the liquid at from 0.5 wt % to 20 wt %, though final latexsolids concentration in the ink is also relevant to the presentdisclosure. Such polymeric particulates can comprise a plurality ofmonomers that are typically randomly polymerized, and can also becrosslinked. Additionally, in one embodiment, the latex component canhave a glass transition temperature from about −20° C. to +100° C.

Generally, any latex polymer commercially available can be used in theinks of the present disclosure including self-dispersed andfunctionalized latex polymers. Latex polymers can be prepared using anyof a number of known emulsion polymerization techniques whereco-monomers are dispersed and polymerized in a discontinuous phase of anemulsion. Monomers that are often used include ethyl acrylate; ethylmethacrylate; benzyl acrylate; benzyl methacrylate; propyl acrylate;propyl methacrylate; iso-propyl acrylate; iso-propyl methacrylate; butylacrylate; butyl methacrylate; hexyl acrylate; hexyl methacrylate;octadecyl methacrylate; octadecyl acrylate; lauryl methacrylate; laurylacrylate; hydroxyethyl acrylate; hydroxyethyl methacrylate; hydroxyhexylacrylate; hydroxyhexyl methacrylate; hydroxyoctadecyl acrylate;hydroxyoctadecyl methacrylate; hydroxylauryl methacrylate; hydroxylaurylacrylate; phenethyl acrylate; phenethyl methacrylate; 6-phenylhexylacrylate; 6-phenylhexyl methacrylate; phenyllauryl acrylate;phenyllauryl methacrylate; 3-nitrophenyl-6-hexyl methacrylate;3-nitrophenyl-18-octadecyl acrylate; ethyleneglycol dicyclopentyl etheracrylate; vinyl ethyl ketone; vinyl propyl ketone; vinyl hexyl ketone;vinyl octyl ketone; vinyl butyl ketone; cyclohexyl acrylate;methoxysilane; acryloxypropyhiethyldimethoxysilane; trifluoromethylstyrene; trifluoromethyl acrylate; trifluoromethyl methacrylate;tetrafluoropropyl acrylate; tetrafluoropropyl methacrylate;heptafluorobutyl methacrylate; iso-butyl acrylate; iso-butylmethacrylate; 2-ethylhexyl acrylate; 2-ethylhexyl methacrylate;iso-octyl acrylate; and iso-octyl methacrylate.

The latexes used herein can be prepared by latex emulsionpolymerization, and, in one embodiment, can have a weight averagemolecular weight from 10,000Mw to 5,000,000 Mw. This range is onlyexemplary and can be broader. Co-polymers can be formed, including blockcopolymers, randomly assembled copolymers, copolymers includingcrosslinkers, or the like. Often the copolymer is a randomly assembledcopolymer, though various subclasses of each polymer type can be used,e.g., core-shell, various glass transition temperatures, surface acidgroups, crosslinking, etc. It is noted that it is not the purpose of thepresent disclosure to describe all different types of latexes that canbe used. Thus, the description of such latexes should not be consideredlimiting with respect to type of dispersed polymer that can be used.

It should be noted that the preparation of a latex, which includes thelatex particulates and a liquid phase, and the preparation of an ink-jetink that includes a latex, can be carried out in many different ways. Inone embodiment, the liquid phase of the latex and a liquid vehicle of anink can become admixed to form a modified liquid vehicle containinglatex particulates and colorant. When the colorant is a self-dispersedor conventionally dispersed pigment, the total solids content of thelatex particulates and pigments can be considered when determiningrelative amounts that should be present for jettability purposes.

Liquid Vehicles

In accordance with embodiments of the present disclosure, the liquidvehicle includes a phosphate-containing surfactant. Other ingredientsthat can be present include water, organic co-solvents, othersurfactants, biocides, sequestering agents, etc. With respect to thephosphate-containing surfactant, the phosphate surfactant can be aphosphate ester of fatty alcohol alkoxylates. In one embodiment, thesurfactant can be a mixture of mono- and diesters, and can optionallyhave an acid number from 50 to 150. In another embodiment, thephosphate-containing surfactant can be of the Crodafos family. Specificexamples include oleth-3 phosphate, oleth-10 phosphate, oleth-5phospahte, dioleyl phosphate, ppg-5-ceteth-10phosphate, C₉-C₁₅ alkylmonophosphate, deceth-4 phosphate, and mixtures thereof. Other specificexamples by tradename include Crodafos N3A, Crodafos N3E, Crodafos N10A,Crodafos HCE, Crodafos SG, Arlantone Map 950, Monofax 831, Monofas 1214,Monalube 215, and Atlox DP13/6.

In further detail with respect to the surfactant, the ink-jet inkcompositions can be substantially free of surfactants other than thephosphate-containing surfactant. However, certain second surfactants canalso be used and may include standard water-soluble surfactants such asalkyl polyethylene oxides, alkyl phenyl polyethylene oxides,polyethylene oxide (PEO) block copolymers, acetylenic PEO, PEO esters,PEO amines, PEO amides, dimethicone copolyols, ethoxylated surfactants,fluorosurfactants, and mixtures thereof. In one specific embodiment, afluorosurfactant can be used as the second surfactant. In anotherembodiment, a secondary alcohol ethoxylated surfactant can be used. Ifused, the second surfactant can be present at from 0.001 wt % to 10 wt %of the ink-jet ink composition, and in one embodiment, can be present atfrom 0.001 wt % to 0.1 wt %.

In the ink-jet inks described herein, suitable co-solvents for useinclude water and water soluble organic co-solvents. Examples of suchwater soluble organic co-solvents include, but are not limited to,aliphatic alcohols, aromatic alcohols, diols, triols, glycol ethers,poly(glycol) ethers, lactams, formamides, acetamides, long chainalcohols, ethylene glycol, propylene glycol, diethylene glycols,triethylene glycols, glycerine, dipropylene glycols, glycol butylethers, polyethylene glycols, polypropylene glycols, amides, ethers,carboxylic acids, esters, organosulfides, organosulfoxides, sulfones,alcohol derivatives, carbitol, butyl carbitol, cellosolve, etherderivatives, amino alcohols, and ketones. For example, co-solvents caninclude primary aliphatic alcohols of 30 carbons or less, primaryaromatic alcohols of 30 carbons or less, secondary aliphatic alcohols of30 carbons or less, secondary aromatic alcohols of 30 carbons or less,1,2-diols of 30 carbons or less, 1,3-diols of 30 carbons or less,1,5-diols of 30 carbons or less, ethylene glycol alkyl ethers, propyleneglycol alkyl ethers, poly(ethylene glycol) alkyl ethers, higher homologsof poly(ethylene glycol) alkyl ethers, poly(propylene glycol) alkylethers, higher homologs of poly(propylene glycol) alkyl ethers, lactams,substituted formamides, unsubstituted formamides, substitutedacetamides, and unsubstituted acetamides. Specific examples ofco-solvents that are preferably employed in the practice of thisinvention include, but are not limited to, 1,5-pentanediol,2-pyrrolidone, Liponic ethoxylated glycerol 1 (EG-1), Liponicethoxylated glycerol 7 (EG-7), 2-methyl-2,4-pentanediol,2-methyl-1,3-propanediol, 2-ethyl-2-hydroxymethyl-1,3-propanediol,diethylene glycol, 3-methoxybutanol, propylene glycol monobutyl ether,1,3-dimethyl-2-imidazolidinone, and derivatives thereof. Co-solvents canbe added to reduce the rate of evaporation of water in the ink tominimize clogging or other properties of the ink such as viscosity, pH,surface tension, optical density, and print quality. The water solubleorganic co-solvent total concentration can range from about 5 wt % toabout 50 wt %. In one embodiment, when multiple co-solvents are used,each co-solvent can be typically present at from about 0.5 wt % to about20 wt % of the ink-jet ink composition. This being said, the solventsmay be present in the ink-jet ink composition at any concentration. Inparticular, the concentration of solvents such as 2-pyrrolidinone andits derivatives may play a role in helping the latex form a durable filmon the vinyl media when used in conjunction with at least one secondaryalcohol ethoxylate and at least one fluoro-surfactant. In an embodiment,the ink-jet ink composition may comprise 2-pyrrolidinone or itsderivatives in combination with a humectant solvent, such as2-methyl-1,3,-propanediol. In other words, the ink-jet ink can comprisea liquid vehicle including a plurality of solvents, and included amongthe plurality of solvents can be from 10 wt % to 30 wt % of a solventsystem consisting of one or more of 2-pyrrolidone, a derivative of2-pyrrolidone, and a humectant, such as 2-methyl-1,3-propanediol.

Various buffering agents can also be optionally used in the ink-jet inkcompositions of the present invention. Typical buffering agents includesuch pH control solutions as hydroxides of alkali metals and amines,such as lithium hydroxide, sodium hydroxide, potassium hydroxide; citricacid; amines such as triethanolamine, diethanolamine, anddimethylethanolamine; and other basic or acidic components. If used,buffering agents typically comprise less than about 10 wt % of theink-jet ink composition.

In another aspect of the present invention, various biocides can be usedto inhibit growth of undesirable microorganisms. Several non-limitingexamples of suitable biocides include benzoate salts, sorbate salts,commercial products such as NUOSEPT, UCARCIDE, VANCIDE, PROXEL, andother known biocides. Typically, such biocides comprise less than about5 wt % of the ink-jet ink composition and often from about 0.05 wt % toabout 2 wt %.

Other known additives can also be included, as is known in the art.

EXAMPLES

The following examples illustrate the embodiments of the invention thatare presently best known. However, it is to be understood that thefollowing are only exemplary or illustrative of the application of theprinciples of the present invention. Numerous modifications andalternative compositions, methods, and systems may be devised by thoseskilled in the art without departing from the spirit and scope of thepresent invention. The appended claims are intended to cover suchmodifications and arrangements. Thus, while the present invention hasbeen described above with particularity, the following examples providefurther detail in connection with what are presently deemed to be themost practical and preferred embodiments of the invention.

Example 1

Twelve ink-jet inks were prepared having the following generalformulations:

TABLE 1a Yellow Inks INGREDIENT Y-L Y-M Y-H Y-0 Yellow pigment 3 wt % 3wt % 3 wt % 3 wt % dispersion 2-methyl-1,3- 9 wt % 9 wt % 9 wt % 9 wt %propanediol 2-pyrrolidone 16 wt % 16 wt % 16 wt % 16 wt %Fluorosurfactant 1 wt % 1 wt % 1 wt % 1 wt % Secondary 0.35 wt % 0.35 wt% 0.35 wt % — alcohol ethoxylate surfactant Phosphate- 0.6 wt % 0.75 wt% 0.9 wt % — containing surfactant Latex dispersion 6 wt % 6 wt % 6 wt %6 wt %

TABLE 1b Cyan Inks INGREDIENT C-L C-M C-H C-0 Cyan pigment 1.61 wt %1.61 wt % 1.61 wt % 1.61 wt % dispersion 2-methyl-1,3- 9 wt % 9 wt % 9wt % 9 wt % propanediol 2-pyrrolidone 16 wt % 16 wt % 16 wt % 16 wt %Fluoro- 1 wt % 1 wt % 1 wt % 1 wt % surfactant Secondary 0.35 wt % 0.35wt % 0.35 wt % — alcohol ethoxylate surfactant Phosphate- 0.6 wt % 0.75wt % 0.9 wt % — containing surfactant Latex 7 wt % 7 wt % 7 wt % 7 wt %dispersion

TABLE 1c Light Cyan Inks INGREDIENT LC-L LC-M LC-H LC-0 Cyan pigment0.54 wt % 0.54 wt % 0.54 wt % 0.54 wt % dispersion 2-methyl-1,3- 9 wt %9 wt % 9 wt % 9 wt % propanediol 2-pyrrolidone 16 wt % 16 wt % 16 wt %16 wt % Fluoro- 1 wt % 1 wt % 1 wt % 1 wt % surfactant Secondary 0.35 wt% 0.35 wt % 0.35 wt % — alcohol ethoxylate surfactant Phosphate- 0.6 wt% 0.75 wt % 0.9 wt % — containing surfactant Latex 4 wt % 4 wt % 4 wt %4 wt % dispersion

As can be seen above, four inks included yellow pigment and latex(Yellow Ink), four inks included cyan pigment and latex (Cyan Ink), andfour inks included a lower pigment load of cyan pigment and latex (LightCyan Ink). Each of the four inks from each ink class included adifferent amount of a phosphate-containing surfactant, i.e. none, high,medium, or low. The coding for each ink color above is notated by Y foryellow, C for cyan, or LC for light cyan. Likewise, the coding for theamount of phosphate-containing in each ink is notated by 0 for nophosphate-containing, H for high concentration of phosphate-containing,M for a medium concentration of phosphate-containing, and L for a lowconcentration of phosphate-containing. It is noted that other colors canalso benefit from the addition of phosphate-containing; and further, thenotations of “high,” “medium,” and “low” are relative terms to thisparticular test, and thus, do not infer that higher amounts or loweramounts cannot be used.

Example 2

The 12 ink-jet inks were loaded into 12 different thermal ink-jetarchitectures and fired initially for baseline readings related tosteady state drop weight (except for C-M, where reliable data was notcollected on this particular run). Then, each ink was printed throughits respective print architecture at 400 million drops per nozzle.

The nozzle size for this particular study was about 20 microns. Thekogation performance was determined by measuring the drop weight anddrop velocity retained after significant volume of ink firing. Thekogation test was also carried out with multiple repeating pens foraverage result. After firing 400 million drops through each nozzle, dropweight and drop velocity data was collected. It is noted that mediaevaluations were conducted on Controltac media. The data is shown belowin Table 2, as follows:

TABLE 2 Initial Drop Weight Drop Weight retained Initial Drop VelocityDrop Velocity retained Steady State after 400 million after 400 MillionSteady State after 400 million after 400 Million Drop Weight Drops perNozzle drops per Nozzle Drop Velocity Drops per Nozzle drops per NozzleInk-ID (ng)* Fired (ng) Fired (approx. %) (m/s) Fired (m/s) Fired(approx. %) Y-0 11 6.6 60 12.1 9.8 81 Y-H 12.2 10.9 89 13.4 11.8 99 Y-M11.7 11.5 98.3 13.6 12.5 92 Y-L 12 10.4 87 13.6 10.4 77 C-0 11.3 4.7 4212.8 11.5 90 C-H 11.6 11.3 97.4 12.5 12.2 98.6 C-M 11.5 11.1 96.5 12.812 94 C-L 11.5 11.2 97.4 12.7 11.6 91.3 LC-0 10.8 8.3 77 12.4 8.8 71LC-H 11.6 11.6 100 13.1 12.7 97 LC-M 11.5 11.4 99.2 13.2 12.9 97.7 LC-L11.5 11.5 100 13.4 13 97 *All Initial Steady State Drop Weights in Table2 are considered to be in the range of “about 11 ng to 12 ng.”

As can be seen in the tables above, the presence of thephosphate-containing surfactant tended to lead to drop weight retentionthat was typically better than inks that did not include thephosphate-containing surfactant. Additionally, drop velocity tended tobe improved (except for Y-L which was similar in result to Y-0) by thepresence of the phosphate-containing surfactant. In addition to the datacollected as described above, the ink-jet architecture was also visuallyinspected. It was confirmed visually that the ink-jet nozzles, in theabsence of the phosphate-containing surfactant, tended to allow greaterbuildup of latex at the surface of the individual nozzles.

Example 3

Four inks were prepared in accordance with Table 3, as follows:

TABLE 3 CYAN CYAN YELLOW YELLOW INGREDIENT INK A INK B INK A INK BPigment dispersion 2.5 wt % 2.5 wt % 2.8 wt % 2.8 wt % Latex dispersion5 wt % 5 wt % 4.5 wt % 4.5 wt % Phosphate-containing — 1 wt % — 1 wt %surfactant 2-pyrrolidone 16 wt % 16 wt % 16 wt % 16 wt % 2-methyl-1,3- 9wt % 9 wt % 9 wt % 9 wt % propanediol Fluorosurfactant 0.5 wt % 0.5 wt %0.5 wt % 0.5 wt % pigment dispersant 0.5 wt % 0.5 wt % — —

As can be seen in Table 3 above, two inks included conventionallydispersed cyan pigment and latex (Cyan Inks A and B), and two inksincluded self-dispersed yellow pigment and latex (Yellow Inks A and B).The “B” inks also included 1 wt % of a phosphate-containing surfactant.

Example 4

The four ink-jet inks were loaded into four different thermal ink-jetarchitecture devices and fired initially for baseline readings relatedto steady state drop weight and drop velocity. Then, each ink wasprinted through its respective print architecture after 400 milliondrops per nozzle were fired. The nozzle size for this particular studywas about 20 microns. The kogation performance was determined bymeasuring the drop weight and drop velocity change. The kogation testcan be carried out with multiple repeating pens for average result.After firing 400 million drops through each nozzle, drop weight and dropvelocity data was collected. It is noted that media evaluations wereconducted on Controltac media. The data is shown below in Table 4, asfollows:

TABLE 4 Drop weight Drop Velocity retained after 400 retained after 400Million Drops Million Drops per Nozzle Fired per Nozzle Fired Ink ID(approx. %) (approx. %) Cyan Ink B 93 83 Cyan Ink A 51 52 Yellow Ink B96 88 Yellow Ink A 79 71

As can be seen in Table 4 above, the presence of thephosphate-containing surfactant tended to lead to drop weight retentionthat was much better than inks that did not include thephosphate-containing surfactant. Additionally, drop velocity tended tobe improved by the presence of the phosphate-containing surfactant. Inaddition to the data collected as described above, the ink-jetarchitecture was also visually inspected. It was confirmed visually thatthe ink-jet nozzles, in the absence of the phosphate-containingsurfactant, tended to allow greater buildup of latex at the surface ofthe individual nozzles.

While the invention has been described with reference to certainpreferred embodiments, those skilled in the art will appreciate thatvarious modifications, changes, omissions, and substitutions can be madewithout departing from the spirit of the invention. It is thereforeintended that the invention be limited only by the scope of the appendedclaims.

1. An ink-jet ink, comprising: from 0.1 wt % to 10 wt % pigment bysolids, from 0.1 wt % to 15 wt % latex by solids, and from 0.01 wt % to3 wt % phosphate-containing surfactant, wherein when the ink-jet ink isfired from a thermal ink-jet printhead at 400 million drops per nozzlewith said nozzle having an orifice size of about 20 microns, at least80% drop weight is retained compared to an initial firing prior tofiring the 400 million drops per nozzle.
 2. The ink-jet ink of claim 1,wherein at least 75% drop velocity is retained compared to the initialfiring prior to firing the 400 million drops per nozzle.
 3. The ink-jetink of claim 1, wherein at least 90% drop weight is retained compared tothe initial firing prior to firing the 400 million drops per nozzle. 4.The ink-jet ink of claim 1, wherein when the ink-jet ink is fired from athermal ink-jet printhead at 400 million drops per nozzle with saidnozzle having an orifice size of about 20 microns, at least 90% dropvelocity is retained compared to the initial firing prior to firing the400 million drops per nozzle.
 5. The ink-jet ink of claim 1, whereinwhen the ink-jet ink is fired from a thermal ink-jet printhead at 400million drops per nozzle at a drop weight of about 11 ng to 12 ng, atleast 80% drop weight is retained compared to an initial firing prior tofiring the 400 million drops per nozzle.
 6. The ink-jet ink of claim 1,further comprising a second surfactant.
 7. The ink-jet ink of claim 6,wherein the second surfactant is a fluorosurfactant.
 8. The ink-jet inkof claim 6, wherein the second surfactant is an ethoxylated surfactant.9. The ink-jet ink of claim 1, further comprising at least one of2-pyrrolidone, derivatives of 2-pyrrolidone, and2-methyl-1,3-propanediol.
 10. The ink-jet ink of claim 9, wherein theink-jet ink comprises a liquid vehicle including a plurality ofsolvents, and included among the plurality of solvents is from 10 wt %to 30 wt % of a solvent system consisting of one or more of2-pyrrolidone, a derivative of 2-pyrrolidone, and a humectant solvent.11. The ink-jet ink of claim 10, wherein the humectant solvent ispresent and is 2-methyl-1,3-propanediol.
 12. The ink-jet ink of claim 1,wherein the pigment is a self-dispersed pigment.
 13. The ink-jet ink ofclaim 1, wherein the phosphate-containing surfactant is present at from0.1 wt % to 2 wt %.
 14. The ink-jet ink of claim 1, wherein thephosphate-containing surfactant is a phosphate ester of a fatty alcoholalkoxylate.
 15. The ink-jet ink of claim 14, wherein the phosphate esterof a fatty alcohol alkoxylate is a mixture of mono- and di-esters. 16.The ink-jet ink of claim 1, wherein the phosphate-containing surfactantis selected from the group consisting of oleth-3 phosphate, oleth 10phosphate, oleth-5 phospahte, dioleyl phosphate, ppg-5-ceteth-10phosphate, C₉-C₁₅ alkyl monophosphate, deceth-4 phosphate, and mixturesthereof.
 17. The ink-jet ink of claim 1, wherein the pigment is presentat from 0.5 wt % to 5 wt % by solids, and the latex is present at from 2wt % to 8 wt % by solids.
 18. A method of ink-jet printing over aprolonged period of time, comprising jetting an ink-jet ink onto a mediasubstrate, said ink-jet ink, including: from 0.1 wt % to 10 wt % pigmentby solids, from 0.1 wt % to 15 wt % latex by solids, and from 0.01 wt %to 3 wt % phosphate-containing surfactant, wherein when the ink-jet inkis fired from a thermal ink-jet printhead at 400 million drops pernozzle with said nozzle having an orifice size of about 20 microns, atleast 80% drop weight is retained compared to an initial firing prior tofiring the 400 million drops per nozzle.
 19. The method of claim 18,wherein at least 75% drop velocity is retained compared to the initialfiring prior to firing the 400 million drops per nozzle.
 20. The methodof claim 18, wherein the ink-jet ink is fired from a thermal ink-jetprinthead at 400 million drops per nozzle at a drop weight of about 11ng to 12 ng, at least 80% drop weight is retained compared to an initialfiring prior to firing the 400 million drops per nozzle, and wherein atleast 75% drop velocity is retained compared to the initial firing priorto firing the 400 million drops per nozzle.
 21. The method of claim 18,wherein the ink-jet ink further comprises a second surfactant.
 22. Themethod of claim 21, wherein the second surfactant comprises at least oneof fluorosurfactant or an ethoxylated surfactant.
 23. The method ofclaim 18, wherein the phosphate-containing surfactant is a phosphateester of a fatty alcohol alkoxylate.
 24. The method of claim 22, whereinthe phosphate ester of a fatty alcohol alkoxylate is a mixture of mono-and di-esters.
 25. The method of claim 18, wherein thephosphate-containing surfactant is selected from the group consisting ofoleth-3 phosphate, oleth 10 phosphate, oleth-5 phospahte, dioleylphosphate, ppg-5-ceteth-10 phosphate, C₉-C₁₅ alkyl monophosphate,deceth-4 phosphate, and mixtures thereof.
 26. The method of claim 18,wherein the ink-jet ink comprises a liquid vehicle including a pluralityof solvents, and included among the plurality of solvents is from 10 wt% to 30 wt % of a solvent system consisting of one or more of2-pyrrolidone, a derivative of 2-pyrrolidone, and a humectant solvent.27. The method of claim 26, wherein the humectant solvent is present andis 2- methyl -1,3-propanediol.